linux-kernel - [PATCH 4.4 78/83] drm/mst: Avoid dereferencing a NULL mstb in drm_dp_mst_handle_up

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Message-Id: <20170725191720.589431103@linuxfoundation.org>
Date:   Tue, 25 Jul 2017 12:19:42 -0700
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Dave Airlie <airlied@...hat.com>,
        Lyude <lyude@...hat.com>, Daniel Vetter <daniel.vetter@...ll.ch>,
        Imre Deak <imre.deak@...el.com>
Subject: [PATCH 4.4 78/83] drm/mst: Avoid dereferencing a NULL mstb in drm_dp_mst_handle_up_req()

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Imre Deak <imre.deak@...el.com>

commit 7f8b3987da54cb4d41ad2545cd4d7958b9a36bdf upstream.

In case of an unknown broadcast message is sent mstb will remain unset,
so check for this.

Cc: Dave Airlie <airlied@...hat.com>
Cc: Lyude <lyude@...hat.com>
Cc: Daniel Vetter <daniel.vetter@...ll.ch>
Signed-off-by: Imre Deak <imre.deak@...el.com>
Reviewed-by: Lyude <lyude@...hat.com>
Signed-off-by: Daniel Vetter <daniel.vetter@...ll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20170719114330.26540-3-imre.deak@intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/gpu/drm/drm_dp_mst_topology.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -2323,7 +2323,9 @@ static int drm_dp_mst_handle_up_req(stru
 			DRM_DEBUG_KMS("Got RSN: pn: %d avail_pbn %d\n", msg.u.resource_stat.port_number, msg.u.resource_stat.available_pbn);
 		}
 
-		drm_dp_put_mst_branch_device(mstb);
+		if (mstb)
+			drm_dp_put_mst_branch_device(mstb);
+
 		memset(&mgr->up_req_recv, 0, sizeof(struct drm_dp_sideband_msg_rx));
 	}
 	return ret;